1. Field of the Invention
The present invention relates to a method and apparatus for writing data to and reading data from a phase-change random access memory (PRAM), and more particularly, to a method and apparatus for reducing power consumption when data are written to a PRAM.
2. Description of the Related Art
Phase-change random access memories (PRAMs) are memory devices for storing data by using the phase change of a material. In a PRAM, a crystalline state and an amorphous state represent bit values ‘0’ and ‘1’, respectively. (The respective representations can be reversed, depending on a device design.) The phase change of a material can be induced by a temperature difference caused by the application of current, and an example of cell materials having such a property include germanium antimony telluride (GST or Ge2Sb2Te5).
PRAMs have nonvolatile characteristics like NAND flash memories. However, PRAMs differ from NAND flash memories in that data can be accessed on a byte basis, and erasing is not necessary. Because of such characteristics, PRAMs are suitable for storage devices in mobile applications.
However, PRAMs consume considerable power during data programming and moreover, the power consumption of PRAMs varies according to a pattern of write data. For example, the power consumption for writing a data bit ‘1’ (or ‘0’) to a PRAM is greater than the power consumption for writing a data bit ‘0’ (or ‘1’) to the PRAM. Hereinafter, it is assumed that the power consumption for writing a data bit ‘1’ to a PRAM is higher than the power consumption for writing a data bit ‘0’ to the PRAM.
FIG. 1 contains a schematic block diagram of a conventional storage device.
Referring to FIG. 1, the conventional storage device includes a processor 110, a buffer memory 120, and a PRAM 130 that are interconnected by a system bus.
In general, the processor 110 receives write data, such as user data A, from the buffer memory 120, such as a dynamic random access memory (DRAM), and writes the user data A to a particular area of the PRAM 130. The processor 110 can add meta-data to the user data A in order to control and receive the user data A. However, in general, the processor 110 writes the user data A to the PRAM 130 without adding metadata. In addition, before writing the user data A to the PRAM 130, the processor 110 may compress the user data A by using a data compression algorithm in order to save storage space of the PRAM 130.
However, it is assumed that the power consumption of the conventional storage device during the operation of writing data is independent of a pattern of the data. The conventional storage device operates under the assumption that the power consumption for writing data to the conventional storage device is independent of the pattern of the data. That is, the processor 110 writes data to the PRAM 130 without considering the pattern (‘0’ or ‘1’) of the data. Therefore, when data are written to the PRAM 130, power is wasted. Additionally, in the case where the user data A is highly compressed data, the size of the user data A may not be effectively reduced through an additional compression process.
Particularly, in mobile applications, it is very important to reduce power consumption. Therefore, there is a need for reducing power consumption by using the power consumption characteristics of a PRAM when programming the PRAM.